Protease-containing liquid detergent compositions are well known. A commonly encountered problem, particularly with heavy duty liquid laundry detergents, is the degradation by proteolytic enzyme of second enzymes in the composition, such as lipase, amylase and cellulase. The performance of the second enzyme upon storage and its stability in product are thus impaired by proteolytic enzyme.
Boronic acids are known to reversibly inhibit proteolytic enzyme. This inhibition of proteolytic enzyme by boronic acid is reversible upon dilution, as occurs in wash water. The inhibition constant (K.sub.i) is ordinarily used as a measure of capacity to inhibit enzyme activity, with a low K.sub.i indicating a more potent inhibitor. However, it has been found herein that not all boronic acids are effective inhibitors of proteolytic enzyme in liquid detergents, particularly heavy duty liquid laundry detergents, regardless of their K.sub.i values. In fact, the class of boronic acids described herein are superior in liquid detergents, contrary to what one would expect.
A discussion of the inhibition of one proteolytic enzyme, subtilisin, is provided in Philipp, M. and Bender, M. L., "Kinetics of Subtilisin and Thiolsubtilisin", Molecular & Cellular Biochemistry, vol. 51, pp. 5-32 (1983). Inhibition constants for boronic acids are provided therein, and boronic acids are cited as subtilisin inhibitors. Low K.sub.i values are said to indicate more effective inhibitors.
One class of boronic acid, peptide boronic acid, is discussed as an inhibitor of trypsin-like serine proteases such as thrombin, plasma kallikrein and plasmin, especially in pharmaceuticals, in European Patent Application 0 293 881, Kettner et al., published Dec. 7, 1988.
European Patent Application Serial No. 90/870212, published November 14, 1990 discloses liquid detergent compositions containing certain bacterial serine proteases and lipases.
U.S. Pat. No. 4,908,150, Hessel et al, issued March 13, 1990 describes liquid detergent compositions containing lipolytic enzymes wherein the stability of the lipolytic enzyme is said to be improved by inclusion of particular nonionic ethylene glycol containing copolymers.
U.S. Pat. No. 4,566,985, Bruno et al, issued January 28, 1986 describes liquid cleaning compositions containing a mixture of enzymes including a protease and second enzymes. The composition also contains an effective amount of benzamidine hydrohalide to inhibit the digestive effect of protease on the second enzymes.
In European Application 0 376 705, Cardinali et al, published Jul. 4, 1990, liquid detergent compositions containing a mixture of lipolytic enzymes and proteolytic enzymes have been described. The storage stability of the lipolytic enzyme is said to be enhanced by the inclusion of a lower aliphatic alcohol and a salt of a lower carboxylic acid and a surfactant system which is predominantly nonionic.
In European Patent Application 0 381 262 Aronson et al, published Aug. 8, 1990, mixtures of proteolytic and lipolytic enzymes in a liquid medium have been disclosed. The stability of lipolytic enzyme is said to be improved by the addition of a stabilizing system comprising boron compound and a polyol which are capable of reacting, whereby the polyol has a first binding constant with the boron compound of at least 500 l/mole and a second binding constant of at least 1000 l.sup.2 /mole.sup.2.
None of these teach or describe the use of aryl boronic acid which has a substitution at the 3-position relative to boron as an unexpectedly superior reversible inhibitor of proteolytic enzyme in liquid detergent compositions to protect second enzymes in the compositions.